Computer or Cell phone Battery goes low and when the computer slows down

Every Time when a Cell phone or a computer battery goes down low you have to plug it back in because you phone or computer will never turn on again.

  In the future if the battery goes dead on the computer or cell phone you do not have to plug it in because the cell phone and the computer will re charge on it's own.

For example if a Computer or cell phone is on 0 % it will just automatically go on 100 % again will out walking back and forth to plug it.

I was using this 3D art software called Blender and I was trying to put a lot of trees in with out slowing the computer down and it did slow the computer down and that is because you put to much trees in the Blender program.

Or if I wanted to add hair to my character that I sculpt it will slow the computer down to. Maybe in the future no matter how much trees I put on the program or how much hair I put on the program the computer will still go fast and never slow down because computers will be more advanced.